Add support for Annotation Processors in the Javac Extension

[PiIsRational]

Changes

Extended the Javac Extension to be able to load annotation processors, while the java code is getting checked
in KeY. This includes creating settings for the Javac Extension, to be able to set the checkers.
Also, the there are changes to the run step of the gradle script
to add (add-export and add-opens) directives to the java runtime such that annotations processors can access the internal java compiler data structures.
This is required to be done by hand when using KeY as a jar and would require the following (or similar) command:

java \
    --add-exports jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED \
    --add-exports jdk.compiler/com.sun.tools.javac.code=ALL-UNNAMED \
    --add-exports jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED \
    --add-exports jdk.compiler/com.sun.tools.javac.main=ALL-UNNAMED \
    --add-exports jdk.compiler/com.sun.tools.javac.model=ALL-UNNAMED \
    --add-exports jdk.compiler/com.sun.tools.javac.processing=ALL-UNNAMED \
    --add-exports jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED \
    --add-exports jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED \
    --add-opens jdk.compiler/com.sun.tools.javac.comp=ALL-UNNAMED \
    -jar key-2.12.4-dev-exe.jar

Type of pull request

• New feature (non-breaking change which adds functionality)
• There are changes to the (Java) code
• There are changes to the deployment/CI infrastructure (gradle, github, ...)

Ensuring quality

• I made sure that introduced/changed code is well documented (javadoc and inline comments).
• I have tested the feature as follows:
  • I used it with multiple annotation processors
  • I loaded KeY with various settings to check if and when they are deleted
• I have checked that runtime performance has not deteriorated.

Additional information and contact(s)

@WolframPfeifer is involved in this pull request.

The contributions within this pull request are licensed under GPLv2 (only) for inclusion in KeY.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 50.85%. Comparing base (7d01c6c) to head (73d9619).
⚠️ Report is 625 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #3686      +/-   ##
============================================
+ Coverage     50.48%   50.85%   +0.37%     
+ Complexity    16158    15277     -881     
============================================
  Files          1620     1537      -83     
  Lines         92011    89640    -2371     
  Branches      14705    14134     -571     
============================================
- Hits          46455    45590     -865     
+ Misses        40292    38994    -1298     
+ Partials       5264     5056     -208     

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[wadoon]

One solution to the exports-problem is to start javac in an external process. This means:

1. Writing a main function inside KeY
2. On call, use the current classpath and JRE, and start a new Java process which enters the new main function.
3. Capture the diagnostics in the new process, and send them in a structured way to stdout.
4. Read the stdout in the process spawner.

[WolframPfeifer]

Thanks for this PR, which will allow running Checker Framework checkers (e.g. for Nullness of Ownership) from the KeY GUI directly.

Also, thanks to @wadoon for the initial draft of the external checker, and @PiIsRational for polishing.

I have a few minor complaints about the use of var. When these are fixed, the PR would be ready from my point of view. Also, there is code smell in the unit test (check without assert), but we could also keep it like that.

[PiIsRational]

Why is the listener needed here? It seems to only be used to generate an error message for a corner case (a system without a Java compiler). Would it make sense to therefore remove it?